Back in 2010, I wrote and taught an online introduction to photography class on the popular website reddit. It has 30 lessons, covering everything you need to know to get a solid foundation, from basic optics to composition, vision and post-processing. The class has always been free and ad-free. It has proven extremely popular and has been taken by tens (hundreds?) of thousands of people since then. All the lessons are available to all on the dedicated website (no registration needed):